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(Flexible Sigmoidoscopy, Proctosigmoidoscopy, Proctoscopy, Anoscopy)

Procedure overview

What is a sigmoidoscopy?

A sigmoidoscopy is a diagnostic procedure that allows the doctor to examine the lower one-third of the large intestine. Sigmoidoscopy is helpful in identifying the causes of diarrhea, abdominal pain, constipation, abnormal growths, and bleeding. It may also be used to obtain biopsies and to perform procedures, such as removal of polyps or hemorrhoids. Sigmoidoscopy is also used to screen for colorectal cancer, the second leading cause of cancer deaths in the U.S.

A short, flexible, lighted tube, called a sigmoidoscope, is inserted into the intestine through the rectum into the lower part of the large intestine. Air is injected into the intestine through the sigmoidoscope to inflate it for better viewing.

Several procedures may be used to examine different portions of the large intestine. These include a colonoscopy (examination of the entire length of the large intestine), proctoscopy (examination of the anus and rectum), and anoscopy (examination of the anus only). Please see these procedures for additional information.

Although less invasive X-ray procedures, such as a barium enema, may be used to evaluate the large intestine, these procedures cannot provide the direct visualization of the internal intestine necessary to evaluate and diagnose certain conditions.

Anatomy of the colon

Illustration of the anatomy of the digestive system, adult
Click Image to Enlarge

The large intestine, or colon, has four sections:

  • Ascending colon. This extends upward on the right side of the abdomen

  • Transverse colon. This extends from the ascending colon across the body to the left side

  • Descending colon. This extends from the transverse colon downward on the left side

  • Sigmoid colon. It is named because of its S-shape and extends from the descending colon to the rectum

The rectum joins the anus, or the opening where waste matter passes out of the body.

Screening guidelines for colorectal cancer

Colorectal cancer screening guidelines for early detection from the American Cancer Society recommend that beginning at age 50, both men and women should follow one of the examination schedules below:

  • Annual fecal occult blood test (FOBT) or fecal immunochemical test (FIT) and flexible sigmoidoscopy (FSIG) every five years

  • FOBT or FIT every year

  • FSIG every five years

  • Double-contrast barium enema every five years

  • Colonoscopy every 10 years

Persons with any of the following colorectal cancer risk factors should begin screening procedures at an earlier age and be screened more often:

  • Strong family history of colorectal cancer or adenomatous polyps in a first-degree relative, in a parent or sibling before the age of 60 or in two first-degree relatives of any age

  • Family with hereditary colorectal cancer syndromes, such as familial adenomatous polyposis (FAP) and hereditary nonpolyposis colon cancer (HNPCC)

  • Personal history of colorectal cancer or adenomatous polyps

  • Personal history of chronic inflammatory bowel disease

Reasons for the procedure

A sigmoidoscopy may be used to visualize or diagnose colon polyps, tumors, ulceration, inflammation, hemorrhoids, diverticula (pouches), and strictures (narrowing) in the sigmoid colon. It may also be used to determine the cause of recent changes in bowel habits, lower abdominal pain, itching around the anus, or the passage of blood or mucus in the stool.

There may be other reasons for your doctor to recommend a sigmoidoscopy.

Risks of the procedure

As with any invasive procedure, complications may occur. Complications related to sigmoidoscopy may include, but are not limited to, the following:

  • Persistent bleeding after biopsy

  • Peritonitis (inflammation of the lining of the abdominal cavity)

  • Perforation of the intestinal wall (rare)

There may be other risks depending on your specific medical condition. Be sure to discuss any concerns with your doctor prior to the procedure.

Certain factors or conditions may interfere with a sigmoidoscopy. These factors include, but are not limited to, the following:

  • Use of soap suds enemas prior to the procedure, which irritate the lining of the mucosa

  • Presence of barium from previous tests used to examine the colon (such as a barium enema)

  • Inadequate preparation of the bowel before the procedure

  • Problems that may interfere with the passage of the sigmoidoscope, such as narrowing of the colon, surgical adhesions, or disease, such as chronic inflammatory disease

  • Rectal bleeding, which may interfere with visualization

Before the procedure

  • Your doctor will explain the procedure to you and offer you the opportunity to ask any questions about the procedure.

  • You will be asked to sign a consent form to do the test. Read the form carefully and ask questions if something is not clear.

  • Your doctor will give you specific instructions regarding any fasting or special diet to be followed prior to the procedure.

  • If you are pregnant or suspect that you may be pregnant, you should notify your health care provider.

  • Notify your doctor if you are sensitive to or are allergic to any medications, latex, tape, and anesthetic agents (local and general).

  • Notify your doctor of all medications (prescribed and over-the-counter) and herbal supplements that you are taking.

  • Notify your doctor if you have a history of bleeding disorders or if you are taking any anticoagulant (blood-thinning) medications, aspirin, ibuprofen, or other medications that affect blood clotting. It may be necessary for you to stop these medications prior to the procedure.

  • Your doctor will instruct you about ways to prepare your bowels for the test. You may be asked to take a laxative, an enema, a rectal suppository, and/or drink a special fluid that helps prepare your bowel.

  • Patients with diseases of the heart valves may be given antibiotics before the test.

  • Generally, a sedative or anesthesia is not required before the procedure.

  • Based on your medical condition, your doctor may request other specific preparation.

During the procedure

A sigmoidoscopy may be performed on an outpatient basis or as part of your stay in a hospital. Procedures may vary depending on your condition and your doctor's practices.

Generally, the sigmoidoscopy follows this process:

  1. You will be asked to remove any jewelry or other objects that may interfere with the procedure.

  2. You will be asked to remove clothing and be given a gown to wear.

  3. You will be asked to lie on the procedure table on your left side with your knees bent towards your chest. Alternatively, you may be positioned in the knee-chest position, on your knees with your head and chest bent down, touching the table.

  4. The doctor will conduct a rectal exam to check for the presence of blood, mucus, or fecal matter and to help dilate the anus.

  5. A lubricated sigmoidoscope will be slowly inserted into the anus and advanced into the rectum and lower part of the colon (distal sigmoid colon). After the sigmoid colon is visualized, the sigmoidoscope will be removed.

  6. Sigmoidoscopy may be performed in conjunction with an anoscopy and/or a proctoscopy. If these procedures are performed, an anoscope and/or a proctoscope will be inserted to visualize the lower rectum and/or anal canal.

  7. Although minimal discomfort is associated with the procedure, you may feel a strong urge to have a bowel movement when the sigmoidoscope is inserted. You may also feel temporary muscle spasms or lower abdominal pain during the procedure. Taking deep breaths while the tube is being inserted may help to help decrease the discomfort.

  8. Air may be introduced into the bowel to aid visualization. A suction device may be used to remove liquid feces.

  9. During the procedure, specimens and/or biopsies (tissue samples) may be taken from the lining of the large intestine with a special brush, forceps, or swab.

  10. If a polyp is seen, it may be removed, biopsied, or left alone until a subsequent operation is performed.

  11. After the procedure is completed, the instrument will be removed.

After the procedure

If you were positioned in the knee-chest position during the procedure, you should lie on your side or back for a few minutes before getting up from the table. You should move slowly when standing up in order to avoid dizziness from having your head down during the procedure.

You may resume your normal diet and activities, unless otherwise instructed.

If a biopsy or polyp removal was done during the procedure, you may notice a small amount of blood in your bowel movement. This bleeding should stop within a day or so.

You may experience excessive flatulence (passing of gas) and gas pains after the procedure. This is normal. Walking and moving about may help to ease any discomfort.

Notify your doctor to report any of the following:

  • Fever and/or chills

  • Bleeding from the rectum that lasts longer than a day

  • Abdominal pain and/or bloating

  • Inability to pass gas

Following a sigmoidoscopy, your doctor may give you additional or alternate instructions after the procedure, depending on your particular situation.

Online resources

The content provided here is for informational purposes only, and was not designed to diagnose or treat a health problem or disease, or replace the professional medical advice you receive from your doctor. Please consult your health care provider with any questions or concerns you may have regarding your condition.

This page contains links to other websites with information about this procedure and related health conditions. We hope you find these sites helpful, but please remember we do not control or endorse the information presented on these websites, nor do these sites endorse the information contained here.

American Cancer Society

American College of Gastroenterology

American Gastroenterological Association

National Cancer Institute (NCI)

National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)

National Institutes of Health (NIH)

National Library of Medicine